The use of various silicone containing compositions to control foaming (i.e., as antifoams or defoamers) is known. In this regard, it is well established that this art is highly unpredictable and slight modification can greatly alter perforance of such compositions. Most of these compositions contain silicone fluid (usually dimethylpolysiloxane), often in combination with small amounts of silica filler. Additionally, these compositions may include various surfactants and dispersing agents in order to impart improved foam control or stability properties to the compositions. Thus, for example, Rosen, in U. S. Pat. No. 4,076,648, teaches self-dispersible antifoam compositions consisting essentially of a lipophilic nonionic surface active agent homogeneously dispersed in a non-emulsified diorganopolysiloxane antifoam agent. This combination is said to promote dispersibility in water without the need for emulsification.
Kulkarni et al., in U.S. Pat. No. 4,395,352, improved upon the compositions disclosed by Rosen, cited supra, by limiting the viscosity of the dimethylpolysiloxane oil therein to the range of 5,000 to 30,000 cS at 25 C. Such a limitation, it is taught, unexpectedly resulted in improved efficiency in difficult-to-defoam aqueous systems, such as those which contain high concentrations of ionic surfactants and those which are very viscous.
Keil, in U.S. Pat. No. 3,784,479, discloses foam control compositions which consist essentially of a base oil selected from polyoxypropylene polymers, polyoxypropylene-polyoxyethylene copolymers or siloxane-glycol copolymers, a foam control agent, comprising a liquid dimethylpolysiloxane and silica filler, and a dispersing agent which consists of a copolymer of a siloxane resin and a polyoxyalkylene polymer. The contribution to the art in this case is stated to be improved compatibility with otherwise desirable diluents without resorting to emulsifying the foam control agent in water.
In a closely related patent, U.S. Pat. No. 3,984,347, Keil discloses foam control compositions which consist essentially of a base oil selected from polyoxypropylene polymers, polyoxypropylene-polyoxyethylene copolymers or siloxane-glycol copolymers, a foam control agent comprising a liquid dimethylpolysiloxane and silica filler and a siloxane copolymer dispersing agent. This time the dispersing agent consists of a copolymer of a dimethylpolysiloxane polymer and a polyoxyalkylene polymer. The same advantages as reported for U.S. Pat. No. 3,784,479, cited supra, were obtained.
A process for control of foaming in non-aqueous systems is disclosed by Lomas in U.S. Pat. No. 4,460,493. The compositions employed consist essentially of (1) at least one foam control agent, selected from polydimethylsiloxane or poly(methyl-3,3,3-trifluoropropyl)siloxane, which may optionally include a minor portion of a siloxane resin, (2) a dispersing agent of the type described in the patents to Keil, cited supra, and (3) a non-ionic surfactant having an HLB number greater than 10. This invention is said to provide an effective and cost efficient foam control method for the non-aqueous systems described. A similar composition containing a high molecular weight polydimethylsiloxane was also shown to be useful in defoaming highly acidic aqueous systems by Schiefer in U.S. Pat. No. 4,762,640.
German Patent No. 1,444,314, to Farbwerke Hoechst AG, discloses wetting agents based on phosphoric acid esters of aliphatic alcohols which further contain methylpolysiloxanes as antifoaming agents.
European Patent Application 273,448 to Union Carbide Corp., published Jul. 6, 1988, teaches a foam suppressant composition made by a free-radical polymerization of a mixture of diorganopolysiloxanes, silica and a free-radical initiator, wherein the reaction product is diluted with a low viscosity polysiloxane.
More recently, Aizawa et al., in U.S. Pat. Nos. 4,639,489 and 4,749,740, the disclosures of which are hereby incorporated by reference, teach a method for producing a silicone defoamer composition wherein a complex mixture of polyorganosiloxanes, filler, a resinous siloxane and a catalyst to promote reaction of the other components is heated at 50.degree. C. to 300.degree. C.
McGee et al., in Australian Application for Patent No. 34059/89, published Nov. 9, 1989, combine the above mentioned compositions of Aizawa et al. with particular silicone glycol compounds to provide improved antifoams for use in high pH aqueous systems, particularly pulp mill liquors.
Starch, in U.S. Pat. No. 4,983,316, discloses silicone antifoam emulsions particularly suited for controlling foaming in aqueous detergent systems. In this patent, the above mentioned compositions of Aizawa et al. are used in conjunction with a secondary silicone antifoam agent and dispersed in a polypropylene glycol continuous phase.
Terae et al., in U.S. Pat. No. 4,465,849, disclose a method for preparing silicone emulsions from organochlorosilanes by slowly adding the latter to an aqueous medium containing a surface active agent. Although the method taught by Terae et al. represents an advancement in the art, the organochlorosilanes used therein present several drawbacks which limit their utility in antifoam applications. First, the organochlorosilanes are generally soluble in most silicone or organic liquid phases and therefore could not be emulsified therein, as they are in water in the method of Terae et al. Second, the silicon-bonded chlorine on the organochlorosilanes is a highly reactive moiety which would react with fillers and various organic or silicone continuous phases of antifoam emulsions and thus would limit general applicability of these systems. Moreover, fillers such as silica could not be easily suspended in the organochlorosilanes due to their low viscosity. Third, since particle size and particle size distribution is often critical to the performance of a given antifoam emulsion system, the method disclosed by Terae et al. is at distinct disadvantage because it offers little control over these parameters.